OTA - One Transistor Amplifier

[jacco vermeulen]

Isn't it 5 Ohms ?

In Holland we have a saying: If you fart, upupa may come out.

 

[Mad_K]

This is a Common Drain implementation, not Common Source. If it where, your're quite right the out z would be 5R. As Jorge said, out z of a CD circuit is 1/gfs. I'm not shure what it is at 2,6A, but it is more than 0,4S...

 

[steenoe]

And what is impedance of 5 R resistor

I am not the clever one here, but normally I would measure a resistors resistance. Not the impedance, as that complies to the hole circuit🙂

Steen🙂

 

[Tube_Dude]

And what is impedance of 5 R resistor ? Isn't it 5 Ohms ? 😎

Yes, its is...but the 5 Ohms resistor is in parallel with the intrinsic source output impedance of the mosfet.

In a nutshell , the output impedance is 1/Gm in parallel with 5 Ohms...😎

 

[Upupa Epops]

Single ended class " A " amp is from DC look voltage divider 1:1. If bottom part of this divider have " impedance " 5 Ohms, the same must be upper side impedance. Output impedance of this divider is " bottom " side in parallel with " upper " side = 2.5 Ohm...

 

[Tube_Dude]

Single ended class " A " amp is from DC look voltage divider 1:1. If bottom part of this divider have " impedance " 5 Ohms, the same must be upper side impedance. Output impedance of this divider is " bottom " side in parallel with " upper " side = 2.5 Ohm...

See the output impedance of a similar circuit...and tell me the diferences.please! 😉

http://sound.westhost.com/project83.htm

Bandwidth (-3dB) is from 4Hz to 250kHz. Rise time is 1.5 us. Output resistance 0.16 Ohm.

 

[Mad_K]

It's an impedance divider, so it's 5R in paralell with 1/gfs of the mosfet.

 

[Upupa Epops]

Yes, you are right, it is really 1/ Gm.... mea culpa... . But load impedance must be much more higher, than theoretical value - the same like in cathode follower, where it must be cca 100 times higher than theoretical....

 

[Mad_K]

Here's how it looks like 😉

 

[Mad_K]

back

 

[Mad_K]

Inside, don't pay attention to the colors of the wires 😀

 

[Mad_K]

I used a PCB, but this amp is better do just p2p. The reason is that this is my revised SEWA (Rev.1) chassis, and it uses a pcb of this size. So now it was just to pop in this instead to have a listen 😉

 

[Tube_Dude]

Inside, don't pay attention to the colors of the wires 😀

I like that, short and direct connections! 🙂

But it was a good idea, to twist the wires , that come from the transformer secondary , to the rectifier bridge...😎

 

[Mad_K]

Now it's time to sit back, pop a few beer's and listen to records until the grey morning

 

[Tube_Dude]

Now it's time to sit back, pop a few beer's and listen to records until the grey morning

 

[Upupa Epops]

Nice work 😎

 

[hifryer]

MadK,

Where can one get such cases?

thanks

 

[Mad_K]

It is from Fisher-Elektronik. http://www.fischerelektronik.de/
They have some nice cases and a good range of heatsinks 😉

 

[Tyimo]

Hi MadK!

How do you like your amp compared to another Zen amps?
What is your favorite?
Do you still listen your old SOZ?

Greets:

Tyimo

 

[steenoe]

Nice amp, Mads🙂 Good work.

Steen😎